1. Field of the Invention
The present invention relates to a blank or part sensing system for sheet metal forming tools that permits sensing the presence of a blank or part during a forming process.
2. Background Art
Metal parts may be formed in sheet metal forming process in which a blank is formed in a series of steps into a finished part. Several presses may be arranged and aligned to sequently form a part. Parts may be initially drawn in a draw die, and then may be spanked, trimmed, and punched in subsequent press forming operations. The sheet metal parts may also be made in a transfer press in which a die having multiple stations is operated by a single press that has a die with multiple stations that perform prescribed steps in sequence to form a finished part.
Sensors are used in sheet metal forming processes to control the operation of one or more presses. Sensors may be provided in the dies and also may be provided on loaders, shuttles, conveyors and other material handling equipment that is used to load blanks or partially formed parts. Different types of sensors may be used in sheet metal forming processes include limit switches, reed switches, Hall Effect switches, or proximity sensors.
One application for a sensor used in a sheet metal forming tool is as a blank or part presence detector. A part presence detector is used to detect whether a sheet metal blank or a partially formed part is in the proper position for performing the next operation. If a part presence detector provides a false indication that a part is in the desired position the part, die, or tool may be damaged if, in fact, the part is out of location. If a part is mishit by a sheet metal forming tool the part may be scrapped and the tool may be damaged. If a part presence detector indicates the presence of a panel when no panel is in the tool, the tool may be damaged. If a sheet metal forming tool is cycled without performing the desired the operation on the part, the number of parts produced may be inaccurately reflected.
Variations in the strength or resiliency of a blank or part may result in unexpected spring back in the part after a forming operation. Bowed blanks or parts may be difficult to sense by a part presence detector since the blank may be bowed in an area where the sensor is oriented to detect the presence of the blank.
High speed production lines have short cycle times that afford less time for a blank or part to nest within the tool. Less time is also available for sensing that the part is properly nested in the tool. Some part shapes present challenges for locating sensors that accurately and quickly sense the location of a blank or part.
In some instances, it would be advantageous to provide a part presence detector that senses the presence of a part throughout a forming process even as the edge of a part moves during the drawing or forming cycle.
There is a need for an accurate system for sensing the presence of a blank or part. There is a further need for a part sensing system that provides a quick response and is capable of providing an accurate indication of the presence of a part throughout a forming cycle. By providing an improved part presence detecting system a reduction in false signals from the part sensing system can result in reduced downtime and scrap.
The above problems and needs are addressed by applicant's invention as summarized below.